@Crow Hunter: See link above and consider the following.
1: These rounds are not much heavier... many of them are similar in weight to or lighter than AK-47 rounds. The important thing is that their marginal weight increase (which is very small) yields deadlier internal ballistic performance.
All of the rounds that you have listed other than the 5.45X39 are heavier per round than the 5.56, to carry the same number of rounds, someone will have to carry more weight, or reduce the number of rounds carried.
2: These rounds do not recoil a very noticeable amount more than 5.56x45 (many of them akin to AK rounds or less). And, again, they offer better ballistic performance that doesn't rely on high velocities that 5.56x45 never reaches out of a 16", 14.7", or shorter barrel.
I disagree significantly. Other than the 5.45, all of them recoil more, some substatially more than the 5.56. (Beowulf/Socom) I personally did a comparison of a lightweight HK416 with a 10.5 bbl to a Milled Hungarian AK. At 25 yards with the happy switch set to Rock & Roll, at best I could keep 3 rounds on a person sized target with the AK, with the much lighter 416 I could keep 10 to 15 rounds on the target in one burst. Within 8 rounds, the AK was about to shoot over the berm and the AK has a much slower rate of fire.
3: Some of these rounds offer a flatter trajectory than the 5.56 (6.8 to name one). Others might not be as flat but they are adequately flat out to 300m and they are much more effective when they get there.
I figured the 6.5 would have the flatest trajectory, but other than that and the 5.45 most of the others will have near rainbow trajectories. Particularly the 7.62 rounds and the Beowulf/Socom. You can't beat physics, even with a cool name. 
4: Penetration is pointless if it overpenetrates before yawing/fragmenting. These other rounds don't have problems penetrating and have tangible affects on soft targets.
Define "tangible effects". The 7.62X39 is well known for it's penetration but it is also similar to a .38 Special on soft targets it penetrates too far before starting to tumble. Anything similar in velocity/sectional density will have similar effects on the target unless you use a different bullet design. Back to physics again.
5: Well, if one of these rounds is adopted it will be available... so this is a moot point. We are talking about "better" not "most common".
If you are talking about some future condition that doesn't yet exist, you could also theorize that utilizing superior bullet construction in the 5.56 could also happen. The 50gr TSX round is a phenomenal penetrator and has dramatic effects on soft targets, what if you were comparing the TSX to FMJ 6.8SPC? I was speaking in today's terms, with a civilian mindset, not future "what if" terms.
6: If one of these rounds is adopted then it will also cost very little... so this is a moot point. Again, we are talking about "better" not "cheapest"
Again with the "IF". If we aren't talking about today, anything is possible. Including a Phased Plasma Rifle in the 40 Watt range.
7: Lethality. It is lethal, but a .22lr is lethal, too (don't get me wrong... I'm not equating them). I'm just saying that 5.56x45 isn't as deadly as these other rounds and they do not suffer as many of the downsides of using a full house caliber like a .308 (which you claimed that they do judging by your list). They aren't that heavy, they don't recoil that much more, they penetrate better, they do not suffer a loss in magazine capacity
Ummm, yes they do, with the exception of the 5.45, unless you are talking about changing the magazine envelope, some of them (Beowulf/Grendel) reduce it significantly. You can't take a box that holds 30 .22" diameters and stick 30, .30" diameters or .45" diameters in it. That physics thing again. (generally), etc. They aren't 7.62 NATO rounds even though some of them are .308" in diameter.
How do you know that the 5.56 isn't as deadly as the others? Remember, there is no magic bullet. A bullet has to hit a vital area on a target to take it down. A 5.56 through the interoccular cavity will drop someone just as fast as a .50 Beowulf. The difference is getting back on target to shoot the next guy with the 5.56 vs the other rounds.
You seem to be an intelligent guy who is willing to do research. Get an account over at Lightfighter.net, don't ask this question there, but do some research. The guys there do this stuff for a living, some of them are ACTIVELY working with the Asymetric Warfare Group, PEO Soldier, and outfits that "don't exist" developing and testing new rounds & weapon systems in combat. See what they think about the 5.56 vs the .308 and other rounds. You might be suprised what their conclusions are.
The quick answer, those guys are finding that it takes just as many rounds of 7.62X51 from a SCAR H to drop someone as it does with a 5.56 from a SCAR L or M4. The difference is they can't carry as many rounds.
